The present invention pertains to electric motors in which the stator element is formed from a laminated assembly of generally circular plates and, more particularly, to such an assembly in which the plate edges are partially truncated or squared and randomly oriented in a circumferential direction during assembly such that the effective outer surface of the plate stack is maintained cylindrical.
It is well known in the art to construct the stator element of an electric motor from a stack of thin plates in a laminated configuration. The plates have a circular center opening defined by radial stator legs which, in the assembled stack, define a circular inner opening for the rotor. The radial outer peripheral surface of the stack is typically enclosed in a motor housing or shell. When circular plates are utilized, the interior of the housing or shell is generally cylindrical in shape. It is also known to trim or square the edges of the plates to save material, but to leave circular peripheral edge sectors between the trimmed edges which sectors are aligned in assembly to provide semicylindrical surface portions supported directly by the cylindrical interior of the housing. The square trimmed edges are likewise aligned in the assembled stack to provide open outer cylindrical segments for the passage of cooling air between the plate assembly and the inside of the housing or shell. However, the lack of a fully continuous cylindrical outer surface in this plate assembly requires the use of a heavier outer housing or frame and also the possible need to machine or otherwise form tenons on the inside of the housing to achieve good concentricity in the assembled stator.
U.S. Pat. Nos. 1,156,639, 1,158,495 and 2,818,515 all disclose stator assemblies utilizing stacks of laminated plates having squared outer edges separated by circular peripheral edge sectors which circular edges bear against the cylindrical inner face of the motor housing. These patents also show the use of small thinner element substacks which are circumferentially indexed to offset the circular edge portions and provide more continuous support for the cylindrical inside surface of the frame. Although such constructions provide somewhat increased internal support, alignment of the plates in each substack and careful indexing of adjacent substacks making up the entire stator assembly require the use of more sophisticated assembling techniques and equipment.
It is also known to form laminated rotor assemblies for electric motors with circular rotor plates which are randomly oriented to eliminate a buildup of edge thickness variations in the plates over the full width of the plate stack. As indicated, however, rotor plates, unlike stator plates, have completely circular outer peripheral edges and randomizing is easily accomplished utilizing any one of several known techniques.